A long time ago, I at the time (33M), came home from work early and noticed the house empty. I put my things down and was relieved to not have to deal with something the moment I walked in.

I start heading upstairs and hear my stepdaughter making what sounds like, sounds of pain. I hurry up and once I got a few feet from her door, I realized the sounds weren't what I initially thought. I stopped and listened more and realized they were the sounds of sex. She (18F) had a new boyfriend and put two and two together.

I was relieved that nothing bad was happening but at the same time shocked and kind of pissed. I was shocked that she was sleeping with him so soon and pissed that she'd do this under my roof. At the same time, hearing her voice make those sounds turned me on like I couldn't believe.

My heart was pounding and this mix of emotions hitting me like this was a bit much. I stood there for a minute contemplating what the right thing to do was, all the while, listening to what sounds like her getting the pounding of a lifetime. I decided to not intrude or make a scene and just go to my room and change.

I start getting undressed to put on my lounge/house clothes and notice I have a full erection and it's dripping precum. I shouldn't be aroused by this, and I shouldn't feel jealous, but I did. I couldn't stop thinking about it. The sounds especially were so hot, I couldn't shake it off. Since I was alone at the moment, I dove into bed and began jerking myself imagining the forbidden and taboo. I came almost instantly and cleaned up and got into my house clothes. I was still struggling with the emotions and trying to process them.

My door opens and it's her. She's surprised that I'm home and was startled.

"I was headed to the bathroom and saw your door shut, so figured you or mom was back home. Are you ok?" She said as her face flushed.

"Yeah, I just wasn't feeling well at work and figured I'd come home." I replied.

She looks down as if embarrassed and asks if I need anything and I tell her I'm fine. She slowly closes the door. A few minutes later I can hear her boyfriend leaving, which lets me know that this was planned for when her mother and I were at work.

She comes into my room again. Still looking ashamed and flushed. She asked if everything was ok.

"Yeah, everything is fine." I say it in a way that lets her know that I knew her boyfriend was there but I'm not pointing it out deliberately.

She asks, "are you sure?"

I give her a sad look and tell her it is and look away. She knows I know but she also knows I'm not wanting to turn it into an issue. She knows I won't tell her mother.

A bit later she brought me a glass of ice water that I didn't ask for and joined me in watching TV. I'd glance over at her imagining what she'd done, and waves of jealousy and arousal kept going over me. I tried not to act different but I could tell that she knew that I knew more than I was leading onto.

When it got close to time for her mother to come home, she gave me a peck on the cheek and told me she loved me. I smiled and told her that I loved her too.

That night I tried to have sex with her mother (my wife) but she wasn't having it, which was typical at this point in the relationship. So, I laid there thinking of my stepdaughter with a throbbing hardon while lying next to her sleeping mother.